The first sin recorded in the Bible happens at the very beginning, in Genesis, when the woman created by God takes and eats an apple from the one tree she and the man were instructed not to eat from. This starts the fall of mankind, creating separation between God and us. Humanity in need of a Savior. We are all sinful by nature, from the time of our birth to the time of our death. Sin will be part of our world until Jesus' 2nd coming. This may seem discouraging, but the truth is that God loves us anyway. He's knows who we are because he created us. He's not expecting our perfection, just our faith in his unending grace and forgiveness.
Romans 3:23-24 23 For everyone has sinned; we all fall short of God’s glorious standard. 24 Yet God, in his grace, freely makes us right in his sight. He did this through Christ Jesus when he freed us from the penalty for our sins.